Acoustic pianos are very old in the art, and in the case of upright pianos, the acoustic piano has developed into a musical instrument that uses a rather standard key action. Generally speaking, a standard key action uses a key tail (the interior end of the key) to actuate a wippen, which then actuates a hammer shank through a jack and a hammer butt. The far end of the hammer shank is affixed to a hammer that strikes the individual string(s) corresponding to the given musical tone for that key. The standard piano action also uses dampers to silence the string(s), until the damper is de-actuated by pressing its corresponding key or by pressing one of two pedals which simultaneously de-actuates all or one section of the dampers.
Electronic pianos are also old in the art, and it is standard in conventional electronic pianos to detect the movement of each of the individual keys by some type of sensor that generates an electrical signal. Some of these sensors are optical in nature, others detect pressure or force induced against the key by a human user. Regardless of the exact method of detection of the key's movement, an electrical signal is produced when each of the keys is actuated, and in some conventional pianos, the velocity of the key's movement is additionally detected to vary the volume or some other characteristic of the tone to be produced by the sound engine of the electronic piano.
A relatively recent development is the combination of an acoustic piano and an electronic piano in which a single musical instrument can operate in two different modes: (1) an acoustic mode utilizing a standard piano action, and (2) an electronic mode utilizing a standard electric piano's components, however, also preventing the actuation of a portion of the acoustic piano's action, thereby inhibiting an acoustic tone from being generated. There are various types of conventional dual-mode pianos, some of which include the entire standard acoustic action of an upright piano, and others that only utilize a portion of a piano's action. For example, U.S. Pat. No. 4,679,477, by Monte, discloses a "silent" electronic keyboard that includes a pivoted "silent hammer," which has its momentum stopped by a "stop rail." The hammer is directly engaged by the key tail of the keys using a cam and follower action.
Another patent, by Nagai (U.S. Pat. No. 4,704,931), inhibits the vibration of the strings of a piano when operated in its "silent mode." A damper is placed against each of the strings so that when the hammer strikes the string, there will be little or no vibration. During normal acoustic playing mode, the damper is pivoted away from the strings, thereby allowing acoustic tones to be generated in the normal fashion.
An upright piano that includes a hammer-stopping mechanism that suppresses acoustic piano sounds is disclosed in Seiler (DE 37 07 591 C1). This hammer-stopping mechanism is referred to in Seiler as a "register rod" and has no effect on the normal operation of the acoustic action when the piano is operating in its acoustic mode. However, when the piano is operated in its "synthesizer" mode, this register rod intercepts the movement of the hammer shank so that the tip of the hammer cannot strike its corresponding string. The register rod is pivotable about a 90.degree. angle between its actuated and non-actuated positions. As related above, in its non-actuated position, the register rod does not interfere with the hammer shank so that the hammer may strike the string when its corresponding key is operated. To actuate the register rod, one of its sides is pulled down or to the side so that the register rod pivots about a 90.degree. angle such that its intercepting surface is placed in a position that will interfere with the movement of the hammer shank when its corresponding key is operated. By so interfering, the hammer shank is intercepted before it can complete its normal full travel, thereby preventing the hammer from completing its full travel and striking the string.
Another combination acoustic and electronic piano is disclosed in Yamaha (EP 0 573 963 A2), which includes a "stopper" that contacts the hammer shank before its corresponding hammer can strike the string. Yamaha discloses a "mechanical sound producing mode" (i.e., an acoustic mode) and an "electronic sound producing mode" (i.e., an electronic mode). The stopper is actuated between a "free position" and a "blocking position," in which the free position does not interfere with the normal operation of the key action so that the hammer may strike its corresponding string. In the blocking position, the stopper will contact the hammer shank before the shank reaches its normal end travel, thereby also preventing the hammer from reaching its end travel so that its corresponding string is not contacted by the tip of the hammer.
The stopper is mainly constructed of a rotatable shaft that is actuated by a motor. The shaft includes three brackets that protrude from one side of the shaft, much like the lobe of a cam. At the farthest tip of these brackets is a cushion that is designed to contact the hammer shank without unduly creating noise. When the stopper is in its "free position," the brackets are pointed in an upward, vertical direction so as to not interfere with the movement of the hammer shank as it approaches from the side. When in the "blocking position," the brackets, having been rotated 90.degree. from the vertical to the horizontal, now intercept the hammer shank so that it cannot complete its normal travel. Each of the three brackets is designed to intercept the hammer shanks of one of the three portions of the piano keys, i.e., the bass, tenor (mid-range), and treble keys, which would correspond to the three different sections of the piano action.
The conventional hammer shank stopping mechanisms are not suitable for all configurations of upright pianos, particularly where the space requirements or connectivity requirements of a particular upright piano cannot be made compatible.